1. Field of the Invention
This invention relates to roadway marking devices, particularly to such devices having internal light sources.
2. Description of the Prior Art
The need to alert motorists of the limits of a roadway and of oncoming road hazards has been longstanding, and has been accentuated with the development of multi-lane high speed highways. In particular, the need to mark traffic lanes has long been appreciated, and various marking techniques have typically included strips of white paint, paint having retro-reflective glass beads mixed therein, as well as raised pavement marker devices which are secured to the roadway at spaced intervals and which include a high efficiency reflector. All such devices suffer the disadvantage that they are not internally illuminated, i.e., that they only become visible when light from an oncoming vehicle is directed toward the device and is reflected therefrom, and thus in many situations do not adequately alert motorists approaching a hidden hazard such as a sudden left turn.
Internally illuminated marker devices to extend the region of visibility have also been previously suggested. For example, U.S. Pat. No. 3,836,275 (Finch) discloses a marking system in which a flexible molded strip of resilient material has disposed therein electrical conductors which may be utilized to power self-illuminating light sources inserted into recesses in the strip. A major limitation of this and other prior art self-illuminated devices is that the roadway must be cut away to allow installation of electrical lines. Generally, a source of electrical power such as conventional utility power lines must also be available nearby. The high cost of such installations has precluded the use of such devices in all except very high hazard areas such as airport runways.